He declined to say whether Juncker thought US president Donald Trump would uphold the Paris Agreement on slowing global warming, but he said Juncker’s meeting with Trump last week, which covered trade and climate, had been “constructive” and “amicable”.

Amber Rudd, the UK’s home secretary, told the BBC also on Thursday that “we want to have a deep and special partnership” with the EU after the UK left the bloc.

Their remarks came after US president Donald Trump denigrated Germany and caused uncertainty over US defence and climate commitments in a series of meetings with EU, Nato, and G7 leaders in Belgium and in Italy last week.

Martin Schulz, her main rival, who hails from the centre-left SPD party, went further, saying Trump had “humiliated” Merkel and that he was “outraged” and “appalled” at the US leader’s treatment of the chancellor.

He said in an op-ed in Der Tagesspiegel, a German daily, that Trump relied on “political blackmail” instead of “international cooperation”.

He also tweeted on Monday that: “The best answer to Donald Trump is a stronger Europe”.

Schinas, the Commission spokesman, noted on Monday that the EU was taking steps on defence and economic integration.

Echoing Merkel’s speech on EU self-reliance, he said: “This is really about making sure Europe is in charge of its own affairs, but, at the same time, Europe is open to the world and we remain always ready to engage”.

He said Juncker wanted EU international development and refugee aid to be considered as a contribution to transatlantic security because it helped to “stabilise” potential conflict zones.

Schinas, like Merkel, also referenced Brexit, saying: “the Commission works for the unity of the 27 member states” vis-a-vis the US and the departing UK government.

Rudd, the UK minister, told the BBC that the UK would not use its contribution to collective security in Europe as a bargaining chip in the Brexit talks.

"We can reassure Mrs Merkel that we want to have a deep and special partnership so that we can continue to maintain European-wide security to keep us all safe from the terrorists abroad and those that are trying to be nurtured in our country”, she said.

Opinion

Vladimir Putin's nightmare of Petro Poroshenko's re-election will be even certain as Ukrainians rally around the flag. Next March's election is not just to elect a new president but also a commander-in-chief to deal with five more years of Putin.